turns out that Powershell is used by default there, and variable substitutions
are different there.
What's worse is that it doesn't seem to fail if something doesn't work as one
would expect.

Previousoly it would make an additional syscall to change permissions, which
is slower than necessary.

…ng a single index.

The motivating example is here: praetorian-inc/noseyparker#179

Previously, it was possible for a trampling herd of threads to consolidate the
disk state. Most of them would be 'needs-init' threads which could notice that
the initialization already happened, and just use that.

But a thread might be late for the party and somehow manages to not get any
newly loaded index, and thus tries to consolidate with what's on disk again.
Then it would again determine no change, and return nothing, causing the caller
to abort and not find objects it should find because it wouldn't see the index
that it should have seen.

The reason the thread got into this mess is that the 'is-load-ongoing' flagging
was racy itself, so it would not wait for ongoing loads and just conclude nothing
happened. An extra delay (by yielding) now assures it either seees the loading state
and waits for it, sees the newly loaded indices.

Note that this issue can be reproduced with:

```
'./target/release/gix -r repo-with-one-pack -t10 --trace odb stats --extra-header-lookup'
```

Related to helix-editor/helix#10660
which runs into object types that are unknown.

I have looked into this and [couldn't find evidence of a new pack-entry type](https://github.com/git/git/blob/0f3415f1f8478b05e64db11eb8aaa2915e48fef6/packfile.c#L1303-L1358)
in the Git codebase.

It also looks like that Git [will never write packs that aren't V2](https://github.com/git/git/blob/0f3415f1f8478b05e64db11eb8aaa2915e48fef6/pack-write.c#L352)
 - initially I thought it might write V3 based on some other criteria.

For now, the thesis is that one would have to be able to mark bad objects
to be able to handle this more gracefully, but all we can do is try to fail.

…1354)

This behaviour is the same as in Git.

Less IO operations, and less that can go wrong.